Thread is one of the most fundamental of fly tying materials, and today there are dozens of fly tying threads available in a wide variety of materials, sizes and strengths. This guide and our handy Fly Tying Thread Comparison Chart will help you choose the thread that's right for you!
The most common fly tying thread materials today are nylon, polyester and GSP (gel-spun polyethylene). Nylon was developed in the 1930’s as a man-made substitute for silk. Made via a continuous extrusion process, nylon is strong, can stretch a bit and takes dyes well making for bright and vibrant colors. Similar to nylon, man-made polyester is made as either a continuous extrusion fiber or as short fiber filaments. Unlike nylon, polyester doesn't stretch and it will break without warning under stress, though it is quite strong. Polyester colors tend to be slightly less bright than nylon. Gel-spun polyethylene (GSP) is made of continuous extrusion fibers and is very strong. GSP's texture is extremely slippery yet flexible. Less popular but still in use are natural threads made of cotton, wool and silk as well as man-made Kevlar and rayon.
Of the top fly tying thread manufacturers, UNI uses both nylon and polyester, Danville uses nylon, VEEVUS has polyester and GSP threads and Wapsi both nylon and GSP products. For fly tying traditionalists, there is also fly tying silk from Pearsall.
Thread is usually sized either by denier or aught (0) size. Denier is a textile industry convention. A particular thread’s denier equals the gram weight of 9,000 meters of thread. Therefore the lighter the thread, the lower the denier and vice versa. Aught (0) size is an older, less accurate definition with the more ‘0’s” indicating finer thread. Therefore, an 8/0 thread which would be measured as 8 zero’s is much finer than a 3/0 thread which would have 3 zero’s as a measurement.
Another dimension of thread is breaking strength which is very important to fly tyers as we want to wrap thread tightly around our hook and not risk breaking it. Recent advances in thread production have led to some light weight threads with comparatively very high breaking strengths. GSP threads definitely have the highest breaking strengths for their weight and the VEEVUS brand from Denmark has developed threads with very high breaking strengths for their size.
We stock dozens of fly tying threads and feature six different brands - Danville, UNI, VEEVUS, Wapsi, Gordon Griffiths and Pearsall. Within each brand we carry all of the most popular materials and sizes. To give you a complete overview of the specifications (size, weight, breaking strength) of the thread we stock, we’ve put together a handy chart for Comparing Popular Fly Tying Thread. Keep a copy by your fly tying bench!